1. Field of the Invention
The present invention generally relates to a traffic signal preemption system and, more particularly, a system and method that provides centralized preemption of traffic signals based on vehicle activity across diverse systems.
2. Background Description
Traffic preemption control systems have been utilized in present day localities to provide preemptive control of traffic signals and to provide traffic flow control for various types of vehicles such as ambulances, police cars, fire trucks, buses, special convoys, and the like, and denoted as emergency vehicles (EV) hereinafter. The term emergency vehicle (EV) is not limiting to only emergency vehicles, but includes any vehicle for which traffic preemption is provided.
In general, traffic signal preemption is a process that allows emergency vehicles to temporarily change the timing plans of traffic signals so that the emergency vehicles do not have to wait for a red light and achieve right of ways.
Referring to FIG. 1, a typical approach has been to provide equipment within the emergency service vehicle 100 that includes a preemption interface 101 and a transceiver 102 that is capable of broadcasting an emergency signal 105 to a transceiver 106 associated with a particular traffic signal controller (TSC) 108. A traffic signal control cabinet 110 houses various equipment that typically includes a communication subsystem 109, TSC 108, a transceiver 106 (or simply a receiver) and a field preemption interface device 107. The TSC 108 typically controls lights at only one roadway intersection. Various modes of communications have been utilized to broadcast the emergency signal 105 such as sensors under the roadway, radio transmissions, infrared signals, ultrasonic signals, all requiring a least a receiver of appropriate type at each intersection along a possible route of EV to receive the emergency signal 105 and a corresponding transmitter in the emergency service vehicle 100.
An emergency vehicle also has communication equipment that provides communication with its fleet management system and dispatch center. Dispatch centers typically provide the initiating directives that place an EV in emergency mode and convey necessary emergency information such as location, directions, other responding services, etc.
A traffic management system 115 may communicate 120 with an individual TSC 108 in order to update timing plans. The TMS includes a communication subsystem (not shown) that provides communication 120 with TSC 108 via communications subsystem 109. This communication 120 is typically through a communications subsystem 109 that is either integral with or proximate to the TSC 108. The communication 120 may involve coax connectivity, Integrated Services Digital Network (ISDN), fiber, copper, dial-up modems running various baud rates, or radio link. The traffic management system 120 typically controls traffic signal controllers within a particular jurisdiction. Multiple traffic management systems may exist within jurisdictions.
Each of these technologies have unique problems such as maintenance issues for under the roadway systems or passing traffic can interfere with infrared signals and ultrasonic signals. Obstructions may also interfere with this technology. Other problems include determining the arrival time of an EV at a particular intersection. Radio control systems utilize signal strength measurements to anticipate arrival times of EVs at intersections; however, preemption of traffic signals too early can lead to impatient drivers proceeding through an intersection causing potential accident risks. Additionally, preemption too late may cause undesirable delays in the EVs progress. Optimizing the coordinating the traffic signal preemption with arrival of the EV is an important consideration in traffic control systems. Additionally, these types of systems are typically dedicated specific components, making them useful only to the agencies that have purchased such systems.
FIG. 2 shows another illustrative variation of recent approaches that includes a differential global positioning system (GPS) in each EV 130. This type of system may include a vehicle CPU 131 that may facilitate the preemption interface, a vehicle communication radio system 132 with radio antenna 133, and a GPS subsystem 134 for receiving and processing GPS signals. The vehicle communication radio subsystem 132 may include various types of technologies and the radio antennas may include multiple distinct antennas for the different types of communications used in the EV 130. In this type of system, the GPS subsystem 134 provides location information to the vehicle CPU 131, which, in turn, provides updates and exchange of status information through the vehicle communication radio subsystem 132 and radio antenna 133 to a TSC 140. These EV components may take on varying arrangements as necessary.
As part of the traffic signal control cabinet (TSCC) 140, a TSC 108 controls operation of the traffic signal and interfaces with an intersection CPU 142 that receives information from a stationary reference GPS subsystem 143 for additional refinement and correction of deviations of GPS position information received from the EV 130 via a radio signal 146. The TSCC 140 also includes a communication radio subsystem 144 and radio antenna 145 for receiving the radio signals 146. Here again, the TSCC 140 typically has a communication subsystem 109, either integral or non-integral, for communicating with a traffic management system 115 in the same manner as discussed previously. Other arrangements and connectivity of cabinet components may exist.
In the GPS type system of FIG. 2, as an EV approaches an intersection, the current location is repeatedly transmitted to the proximate intersection TSC, such as 108. The intersection traffic signal controller receives GPS location data and status information from an approaching EV and can calculate the arrival rate and direction of the vehicle and can subsequently control the preemption of the traffic signals with greater accuracy and with minimized impact on traffic flow.
Now, when any of these above described exemplary systems are deployed, the preemption interaction is solely between emergency vehicle and the intersection traffic controller. Additionally, the technology in use is localized to a given jurisdiction or locality. Accordingly, EVs deployed in a given locality must then comply with the traffic preemption techniques and systems that are in place for that locality in order to receive benefits of any traffic preemption systems. But, on occasion, EVs must traverse into, or through, other localities other than those for which the EV is normally intended to provide emergency or other service. In this case, the type of preemption equipment in the EV may be incompatible with traffic control systems installed at intersections. This, of course, poses many logistical problems and may also attribute to slow response times.
Another limitation of the above systems includes the lack of a centralized traffic management system that is capable of coordinating essentially all EVs and traffic light preemption decisions within a broader geographical area, which may include multiple jurisdictions, multiple fleet management systems, or multiple traffic management systems. Since, generally, all of the above systems communicate only between the EV and a proximate traffic light controller that is local to an intersection, comprehensive coordination of traffic lights along an entire route cannot be provided. Nor, in these systems, can coordination of complementing emergency vehicles (e.g., police and fire trucks together) for a given emergency or similar situation be provided.
The present invention is directed to overcoming one or more of the problems or disadvantages associated with the prior art.